Internal combustion engines have at least one cylinder head which is connected to the cylinder block to form a cylinder. The cylinder head and block also include bores for receiving connecting elements. To accommodate the pistons or the cylinder liners, the cylinder block has a corresponding number of cylinder bores, in which the pistons are guided in an axially movable fashion. The cylinder head conventionally serves to hold the valve drives. To control the charge exchange, an engine requires control elements and actuating devices for actuating the control elements. During the charge exchange, the combustion gases are discharged via at least one outlet opening and the charging of the combustion chamber takes place via at least one inlet opening of the cylinder. Engines often make use of lifting valves as the control elements to control the charge exchange. Lifting valves perform an oscillating lifting movement during the operation of the engine which open and close the inlet and outlet opening. The valve actuating mechanism required for the movement of a valve is referred to as the valve drive. A valve actuating device generally comprises a camshaft mounted on the cylinder head. Valve drives open and close the inlet and outlet openings of a cylinder at the correct times. A fast opening and large flow cross sections are advantageous to keep the throttling losses in the inflowing and outflowing gas flows low, to ensure the best possible charging of the cylinder and an effective complete discharge of the combustion gases.
During the discharge of the exhaust gases into the exhaust-gas discharge system, a backflow of exhaust gas into the cylinders should be avoided. The evacuation of the combustion gases out of a cylinder of the engine during the charge exchange is based substantially on two different mechanisms. In one mechanism, the outlet valve opens when the piston is close to bottom dead center and the combustion gases flow at high speed through the outlet opening into the exhaust-gas discharge system. This high speed flow is due to the high pressure level prevailing in the cylinder toward the end of the combustion and the associated high pressure difference between combustion chamber and exhaust line. This flow process is assisted by a high pressure peak referred to as a pre-outlet shock. The pre-outlet shock propagates along the exhaust line at the speed of sound, with the pressure being dissipated with increasing distance traveled as a result of friction.
In the second mechanism of exhaust gas evacuation, the pressures in the cylinder and in the exhaust line are equalized. The combustion gases are no longer evacuated primarily in a pressure-driven manner but rather are expelled as a result of the stroke movement of the piston.
The pressure losses along the exhaust line, in the flow direction, increase with increasing distance traveled. Minimization of these pressure losses helps to achieve greater exhaust gas evacuation. The minimization of the pressure losses also helps to prevent backflow of exhaust gas from the exhaust passages into the cylinder. Another benefit of reducing pressure losses is providing higher energy exhaust gas to turbines in engines which make use of a turbocharger. Another advantage of improving the exhaust gas flow is that exhaust-gas aftertreatment systems reach their operating temperature or light-off temperature more quickly, which is particularly useful during cold start conditions.
Integrated exhaust manifolds may be used to reduce pressure losses and optimize the exhaust paths. In an integrated exhaust manifold, the exhaust lines of an engine are within the cylinder head. Cylinder heads with integrated exhaust manifolds feature compact design, which permits dense packaging of the drive unit as a whole. Furthermore, said exhaust manifold can benefit from a liquid-type cooling arrangement that may be provided in the cylinder head, such that the manifold does not need to be manufactured from high thermal load and expensive materials. These cylinder heads also reduce the number of components which reduces complexity, cost, and weight. Engines often include a plurality of coolant ducts or at least one coolant jacket is generally formed in the cylinder head. Cooling the exhaust gases provides several benefits. Reduced exhaust gas temperature protects downstream components such as sensors, catalytic converters, and turbines. One particular benefit of integrated exhaust manifolds with liquid cooling is the potential avoidance of increasing fuel usage to reduce high exhaust gas temperature to protect the turbocharger and the catalytic converter, especially for gasoline engines. This increased fuel usage is common practice and negatively affects fuel economy.
In one example, the issues described above may be addressed by an engine having a cylinder head and a cylinder, the cylinder having an outlet opening, the outlet opening being connected to an exhaust passage, the exhaust passage having a cross section which changes in a flow direction, and the cross section having a W-shaped outline at a location. In this way, flow from the cylinder may be optimized by reducing friction and pressure loss creating greater evacuation, reducing backflow, and greater flow energy.
As one example, an engine can be designed with exhaust lines with variable cross sectional shape along the length of the line. This shape can be designed to maximize the flow at various locations in the line. One such shape may be that of a W with curved edges. It has been found that a W-shaped cross section minimizes or reduces the pressure losses as a result of friction. Such an engine would see reduced frictional losses and backflow of exhaust gasses into the engine. Conventionally designed engines without optimally shaped exhaust lines would have greater frictional loss and backflow in comparison.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.